(1) Field of the Invention
This invention relates to the recovery of oil from reservoirs in subterranean sedimentary formations by in-situ combustion, also referred to as "fire flooding".
(2) Description of the Prior Art
In-situ combustion methods for the recovery of oil from subterranean formations are disclosed in the following published texts, which are hereby incorporated by reference. "The Petroleum Reservoir" a Short Course by Selley, Anstey and Donohue, International Human Resources Development Corporation, Boston, Mass., 1981. The textbook "Enhanced Recovery of Residual and Heavy Oils", 2nd Ed. edited by M. M. Schumacher and published by Noyes Data Corporation, Parkridge, N.J., U.S.A., 1980. "Heavy Oil Recovery by in In-Situ Combustion" by Dr. Phillip D. White, Tejas Petroleum Engineers Inc., Dallas, Tex., a paper presented at a Dallas Section S.P.E., Continuing Education Seminar, Spring 1980. "Twenty Years Operation of an In-Situ Combustion Project" by Jenkins and Kirkpatrick, Petroleum Society of C.I.M., 1978. An article entitled "In-Situ Combustion Process--Results of a Five-Well Field Experiment, Southern Oklahoma" by Moss, White and McNeil, Magnolia Petroleum Company, Dallas, Society of Petroleum Engineers of AIME presented at the 33rd Annual Fall Meeting of the Society, Houston, Oct. 5-8, 1958.
The White paper points out that as late as 1979, in-situ combustion projects accounted for only a small proportion of the oil produced by thermal methods. It concludes that one deterrent is that the combustion process requires a much more intense engineering effort than other processes. There is a critical need for well designed equipment for control of the wells, rapid and accurate data accumulation, rapid data analysis and trained field operators. The paper states that only widespread field application of this process can supply these improvements.
Process control is essential and complex. To follow the progress of the burning front and to anticipate operating problems, basic data must be obtained and analyzed including air rate and pressure, water injection rate, gas vent rate in individual wells, casing pressures on production wells, gas analysis, oil and water production rate, temperature measurements. Other data which must be obtained on an infrequent, but regular basis includes oil gravity from each well, oil viscosity from each well, water analysis for chlorine, pH of water, pressure of fall-off tests of injectors. The first group of data allow calculations to be made on frontal movement, combustion efficiency and oxygen utilization. The second set of data allows corrections to be made to the calculated data and to prepare for heat front arrival at a producing well.